1. Field of the Invention
The present invention relates to a disc brake which includes a disc rotor formed from an aluminum alloy and hardened with a ceramic reinforcing material and a component such as a disc brake pad having a back plate which is made of heat-resistant resin and heat-resistant short fibers.
2. Description of the Related Art
In Japan Patent Laid-Open Pub. No. S48-83264, a back plate is disclosed which is made of a synthetic resin. This back plate is made of a synthetic resin, so that it is light, and also it has heat resistance. Thus, attention has been paid to it from early time.
When a brake is operated, kinetic energy of an automobile is converted into friction heat, so that the temperature of a disc rotor is elevated up to 670K or higher. The heat conducts to a back plate via a friction material, so that the temperature of the back plate itself becomes considerably high. Therefore, the heat resistance of the back plate was not sufficient.
Braking is carried out repeatedly with irregular intervals. A friction material of a brake and a back plate are repeatedly exposed to a temperature cycle, so that there was such a problem that deterioration such as crack of material can be generated and the material can have insufficient strength. In addition, in case the difference between a linear expansion coefficient of a friction material and that of a back plate is large, a crack could be generated on an adhesive plane between them.
Therefore, in Japan Patent Laid-Open Pub. No. S57-124134, a back plate is proposed which is prepared by incorporating short fibers such as carbon fibers and glass fibers into a resin back plate and incorporating a continuous fiber prepreg into the center and both ends of the back plate for reinforcement.
It was difficult and not practical, however, to actually produce a back plate having such structure, especially to incorporate continuous fibers which were formed strings. In addition, the composition of a back plate did not become even, and filling fibers to the outer part was insufficient, so that the strength was insufficient.
On the other hand, in recent automobile industry, improvement of fuel performance is strongly advocated. Therefore, in order to lighten a vehicle, use of a disc rotor formed from an aluminum alloy and hardened with a ceramic reinforcing material (here in after xe2x80x9can aluminum alloy disc rotorxe2x80x9d) has been considered for a disc rotor which has been made of steel.
If an aluminum alloy disc rotor is used instead of a steel rotor, a coefficient of friction of the disc brake pad is lowered, so that the brake may work less effectively. Therefore, such a countermeasure has been taken that addition of an abrasive such as alumina to the friction material has been increased. If the amount of abrasive is enhanced, a coefficient of friction increases, so that the brake may work more effectively.
However, if a friction material having a higher coefficient of friction is used for an aluminum alloy disc rotor, loading of the back plate increases, and the back plate tends to be heated, so that it was difficult to secure strength.
The present invention was conceived in order to solve such a problem. It is therefore the object of the present invention to provide a disc brake using an aluminum alloy disc rotor which allows lightening of a brake, has heat resistance, and gives sufficient strength, a disc brake pad for the same, and a back plate used for the disc brake pad.
In order to achieve the above object, according to a first aspect of the present invention there is provided a disc brake which has a disc rotor made of an aluminum alloy and hardened with a ceramic reinforcing material and a disc brake pad which is provided so as to be able to connect and disconnect the rotor, wherein the disc brake pad has a back plate which is made of a heat-resistant resin of organic polymer in which heat-resistant short fibers are incorporated.
To attain the above object, according to a second aspect of the present invention there is provided a disc brake pad which is used for an aluminum alloy disc rotor, wherein the disc brake pad has a back plate which is made of a heat-resistant resin of organic polymer in which heat-resistant short fibers are incorporated.
Preferably, the disc brake pad is prepared by bonding a non-asbestos-based friction material which contains a non-asbestos nonmetallic heat-resistant fiber component, a filler, and a heat-resistant resin, to the back plate.
In order to achieve the above object, according to a third aspect of the present invention there is provided a back plate for a disc brake pad which is used for a disc rotor made of an aluminum alloy, wherein the back plate contains heat-resistant short fibers and an organic polymer based heat-resistant resin.
Preferably, the back plate contains heat-resistant short fibers at 50 wt. % or more, and the heat-resistant short fibers are glass fibers.
The heat-resistant short fibers may have a length of 10 mm or less.
The back plate may have a shrinkage percentage of 0.15% or less upon a heat treatment, and a difference between a shrinkage percentage of the back plate and that of said friction material which is bonded to the back plate is 0.1% or less.
The back plate for a disc brake pad of the present invention is particularly suitable for a brake in a small-sized vehicles or ordinary passengers vehicles with regenerative brake or for a rear brake in ordinary passenger vehicles having a relatively small braking load.